Inter-RAT/frequency automatic neighbor relation list management

ABSTRACT

In one of its aspects the technology concerns a method of operating a telecommunications system comprising a serving radio base station and a candidate radio base station. The serving radio base station comprises a radio base station to which a wireless mobile station provides measurement reports. The serving radio base station and the candidate radio base station are different with respect to at least one of frequency and radio access technology. The method comprises the serving radio base station allowing the mobile station to obtain information broadcasted by the candidate radio base station. The information is either information for locating Cell Global Identity (CGI) of the candidate radio base station or the Cell Global Identity (CGI) itself of the radio base station. The mobile station obtains the information from the candidate radio base station during at least one reading gap. The reading gap is a time period in which the mobile station does not receive information from the serving radio base station.

This application is a continuation of U.S. patent application Ser. No.13/281,818, filed Oct. 26, 2011, pending, which is a divisional of U.S.patent application Ser. No. 12/331,897, filed Dec. 10, 2008 (now U.S.Pat. No. 8,107,950), which claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/023,469, filed Jan. 25, 2008. Each of the abovementioned applications and the above mentioned patent is incorporated byreference.

BACKGROUND

I. Technical Field

This invention pertains to telecommunications, and particularly aninter-radio access technology (IRAT) and inter-frequency measurement(s)involved with neighbor relation list management.

II. Related Art and Other Considerations

In a typical cellular radio system, wireless terminals (also known asmobile stations and/or user equipment units (UEs)) communicate via aradio access network (RAN) to one or more core networks. The wirelessterminals can be mobile stations or user equipment units (UE) such asmobile telephones (“cellular” telephones) and laptops with wirelesscapability), e.g., mobile termination), and thus can be, for example,portable, pocket, hand-held, computer-included, or car-mounted mobiledevices which communicate voice and/or data with radio access network.

The radio access network (RAN) covers a geographical area which isdivided into cell areas, with each cell area being served by a basestation, e.g., a radio base station (RBS), which in some networks isalso called “NodeB” or “B node”. A cell is a geographical area whereradio coverage is provided by the radio base station equipment at a basestation site. Each cell is identified by a identity within the localradio area, which is broadcast in the cell. The base stationscommunicate over the air interface operating on radio frequencies withthe user equipment units (UE) within range of the base stations.

In some versions (particularly earlier versions) of the radio accessnetwork, several base stations are typically connected (e.g., bylandlines or microwave) to a radio network controller (RNC). The radionetwork controller, also sometimes termed a base station controller(BSC), supervises and coordinates various activities of the plural basestations connected thereto. The radio network controllers are typicallyconnected to one or more core networks.

The Universal Mobile Telecommunications System (UMTS) is a thirdgeneration mobile communication system, which evolved from the GlobalSystem for Mobile Communications (GSM), and is intended to provideimproved mobile communication services based on Wideband Code DivisionMultiple Access (WCDMA) access technology. UTRAN is essentially a radioaccess network using wideband code division multiple access for userequipment units (UEs). The Third Generation Partnership Project (3GPP)has undertaken to evolve further the UTRAN and GSM based radio accessnetwork technologies.

Specifications for the Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN) are ongoing within the 3.sup.rd Generation PartnershipProject (3GPP). The Evolved Universal Terrestrial Radio Access Network(E-UTRAN) comprises the Long Term Evolution (LTE) and SystemArchitecture Evolution (SAE).

An inter-radio access technology (RAT) handover is process wherein amobile terminal switches from using a first radio access system having afirst radio access technology (such as GSM) to a second radio accesssystem having a second radio access technology (such as UTRA). Inter-RAThandover is normally initiated when the quality of a downlink radioconnection of the first radio access network falls below a certainlevel. Inter-radio access technology (RAT) handovers are described,e.g., in U.S. Pat. No. 7,181,218, entitled “COMMANDING HANDOVER BETWEENDIFFERING RADIO ACCESS TECHNOLOGIES”, which is incorporated herein byreference in its entirety.

Long Term Evolution (LTE) is a variant of a 3GPP radio access technologywherein the radio base station nodes are connected directly to a corenetwork rather than to radio network controller (RNC) nodes. In general,in LTE the functions of a radio network controller (RNC) node areperformed by the radio base stations nodes. As such, the radio accessnetwork (RAN) of an LTE system has an essentially “flat” architecturecomprising radio base station nodes without reporting to radio networkcontroller (RNC) nodes.

The evolved UTRAN (E-UTRAN) comprises evolved base station nodes, e.g.,evolved NodeBs or eNBs, providing evolved UTRA user-plane andcontrol-plane protocol terminations toward the user equipment unit (UE).The eNB hosts the following functions (among other functions notlisted): (1) functions for radio resource management (e.g., radio bearercontrol, radio admission control), connection mobility control, dynamicresource allocation (scheduling); (2) mobility management entity (MME)including, e.g., distribution of paging message to the eNBs; and (3)User Plane Entity (UPE), including IP Header Compression and encryptionof user data streams; termination of U-plane packets for paging reasons,and switching of U-plane for support of UE mobility. The eNB hosts thePHYsical (PHY), Medium Access Control (MAC), Radio Link Control (RLC),and Packet Data Control Protocol (PDCP) layers that include thefunctionality of user-plane header-compression and encryption. TheeNodeB also offers Radio Resource Control (RRC) functionalitycorresponding to the control plane. The eNodeB performs many functionsincluding radio resource management, admission control, scheduling,enforcement of negotiated UL QoS, cell information broadcast,ciphering/deciphering of user and control plane data, andcompression/decompression of DL/UL user plane packet headers.

2G and 3G systems, including E-UTRAN, make use of Mobile Assistedhandover (MAHO). Each mobile station (MS) periodically monitors thesignal quality of the serving base station (BS) as well as the signalquality of base stations in its surroundings and may report themeasurements back to the serving radio base station. The radio networktypically initiates handovers based on these measurements. As anexample, consider the case of a prepared handover (HO) in E-UTRAN. Thetarget or candidate base station (BS), which the mobile station (MS)will be handed off to, gives guidance for the mobile station (MS) on howto make the radio access, e.g., radio resource configuration andnecessary identities. Further, the serving base station (BS) needs toforward user plane data to the target base station (BS), meaning thatthe target base station (BS) must be known and its unique identity,so-called Cell Global Identity (CGI), must be established beforeexecuting the HO.

Typically, there is also a local identifier (ID) defined for each basestation (BS). The local ID of a base station (BS) is used for layer-1measurements and is not long enough to be unique within the network. Forexample, a mobile station (MS) reports the signal quality of a basestation (BS) along with its local ID to the serving base station (BS).The local ID is not enough for a handover (HO), since the local ID isnot unique within the network. As such, when handing off a mobilestation (MS) to the neighbor the CGI of the neighbor must be known. Theneighbor relation list (NRL), thus constitutes or is at least involvedin the mapping from the local ID to the Cell Global Identity (CGI) andpossibly also other information such as the IP address of the targetbase station (BS).

It is envisioned that E-UTRAN will initially have a limited radiocoverage. To provide seamless mobility it is necessary to Hand Over (HO)mobile stations (MSs) in E-UTRAN to an alternative Radio AccessTechnology (RAT) such as GSM EDGE Radio Access Network (GERAN) or UTRANwith better coverage. It is also desired for a mobile station (MS)served by 2G (e.g. GERAN) or 3G (e.g. UTRAN), to switch to E-UTRAN oncethe mobile station (MS) is within the coverage of E-UTRAN. The latter isdesired since higher data rates are offered by E-UTRAN, enablingservices with greater bandwidth requirements. Handover between twodifferent RATs is referred to as an inter-RAT (IRAT) handover. Further,it is projected that LTE will operate in multiple frequency bands. Tohandle issues like load balancing between different frequency bands,which require inter-frequency handovers (HO), IRAT and inter-frequencyneighbor relation lists (NRLs) are established.

One focus area in E-UTRAN standardization work is to ensure that the newnetwork is simple to deploy and cost efficient to operate. The vision isthat the new system shall be self-optimizing and self-configuring in asmany aspects as possible. See, e.g., 3GPP TR 32.816, Study on Managementof E-UTRAN and SAE.

For inter-RAT/frequency HOs the serving base station (BS) needs to beable to trigger inter-RAT/frequency measurements, make a comparisonbetween different RATs/frequencies, and make a HO decision. Thefollowing events typically need to be performed to prepare for HOs froma serving base station (BS) to a target base station (BS) (e.g. from aE-UTRAN BS to a UTRAN BS) as shown in FIG. 13 (the axses representserving and candidate BS quality): If the estimated signal quality ofthe serving base station (BS) falls below a certain threshold (thresholdA in FIG. 13), then inter-RAT/frequency measurements performed by themobile station (MS) are triggered. If the estimated signal quality ofthe serving base station (BS) rises above a certain threshold (thresholdA in FIG. 13), then inter-RAT/frequency measurements performed by themobile station (MS) are stopped. If the estimated signal quality of theserving base station (BS) is below a certain threshold (threshold A inFIG. 13) and the estimated signal quality of the candidate base station(BS) is above a threshold (B in FIG. 13), then the inter-RAT/frequencyHO procedure may be initiated.

For a mobile station (MS) with a single receiver, the receivingfrequency of the mobile station (MS) has to be altered when carrying outinter-RAT/frequency measurements. When changing the frequency (duringinter-RAT/frequency measurements), the mobile station (MS) is not ableto communicate with the serving RAT. The state during which the mobilestation (MS) carries out inter-RAT/frequency measurements is called thereading gap. The serving base station may avoid transmissions to themobile station (MS) during the reading gap. The state during which abase station does not transmit to a mobile station (MS) is referred toas a transmission gap. Note that, in order for the mobile station (MS)to use the time of the transmission gap for inter-RAT/frequencymeasurements, a reading gap must be issued. From now on, it is assumedthat a reading gap is always issued by the concerned mobile station (MS)when the serving base station (BS) issues a transmission gap. A readinggap can however be issued by the mobile station (MS) even if notransmission gap has been issued by the base station (BS). The gaps mayoccur periodically according to a predefined pattern, as shown in FIG.14, or may be event-triggered. Further, the length of the gaps may befixed or varying.

Some RATs, e.g., E-UTRAN and UTRAN, support dynamic scheduling of uplink(UL) and/or downlink (DL) data, where radio resources are assigned tousers and radio bearers according to the users momentary traffic demand,QoS requirements, and estimated channel quality. The base station (BS)may assign radio resources in time or frequency to mobile stations with,e.g., higher channel quality. The smallest schedulable resource entityis hereafter called a Scheduling Block (SB).

As an example, in E-UTRAN, the scheduling block (SB) comprises twoconsecutive resource blocks, with a total length of 1 ms and width of180 kHz, see FIG. 15. In this case, the base station (BS) allocates SBsto mobile stations both in time and frequency. In E-UTRAN, a mobilestation (MS) may be configured to report Channel Quality Indicator (CQI)reports, indicating the quality of the DL. Based on the CQI reports andQoS requirements the scheduler assigns SBs.

Previously in 2G (e.g., GERAN) and 3G (e.g., UTRAN) systems NRL listshave been populated using planning tools by means of coveragepredictions before the installation of a base station (BS). Predictionerrors, due to inaccuracies in topography data and wave propagationmodels, have forced the operators to resort to drive/walk tests tocompletely exhaust the coverage region and identify all handover regionsand as such the neighbors. Since a radio network gradually evolves overtime with new cells and changing interference circumstances, traditionalplanning of NRL requires iterative repetitions of the planningprocedure. This has proven to be costly and new methods forautomatically deriving NRLs are required. Thus, it is essential to makeuse of automatic in-service approaches for generating and updating NRLs.

The known existing solution aiming at automating NRL management onlyaddress one particular RAT, e.g., GERAN or UTRAN. See, e.g., PCT PatentApplication PCT/EP2007/001737, filed Feb. 28, 2007, which isincorporated herein by reference in its entirety. Even though NRLmanagement has been automated for one type of RAT, the problem ofestablishing NRLs for different RATs/frequencies has not been solvedbefore. Traditionally, these inter-RAT/frequency NRLs have been manuallyderived using topographical information and drive/walk testing. This hasproven to be rather tedious and costly and new automated methods wherethe network itself establishes and configures the NRLs are needed.

What is needed therefore, and an object of this invention, areapparatus, methods, and techniques for establishing and managinginter-RAT measurements and information, such as that utilized by aneighbor relation list for inter-RAT/frequency mobility.

SUMMARY

The technology provides apparatus, methods, and techniques forautomatically managing relationships to neighbors in otherRATs/frequencies, for example neighbor relation lists (NRLs) in E-UTRANcontaining GERAN and UTRAN neighbors. The technology encompasses:Methods & apparatus to detect new inter-RAT/frequency neighbor basestations using mobile station (MS) measurements. Methods and apparatusto retrieve the neighbor base station (BS) CGIs with little or nodisturbance of the ongoing traffic in the serving RAT/frequency. Methodsand apparatus for establishing new neighbors and updating the NRL.

The technology serves, e.g., advantageously to reduce operator expensesfor planning and maintaining inter-RAT/frequency NRLs needed forseamless inter-RAT/frequency mobility.

In one of its aspects the technology concerns a method of operating atelecommunications system comprising a serving radio base station and acandidate radio base station. The serving radio base station comprises aradio base station to which a wireless mobile station providesmeasurement reports. The serving radio base station and the candidateradio base station are different with respect to at least one offrequency and radio access technology. The method comprises the servingradio base station allowing the mobile station to obtain informationbroadcasted by the candidate radio base station; and the mobile stationobtaining the information from the candidate radio base station duringat least one reading gap. The information is either information forlocating Cell Global Identity (CGI) of the candidate radio base stationor the Cell Global Identity (CGI) itself of the radio base station. Thereading gap is a time period in which the mobile station does notreceive information from the serving radio base station.

The information can take various forms. For example, depending on thecontext and timing, the information can be synchronization informationof the candidate radio base station, local identification information ofthe candidate radio base station, information for locating Cell GlobalIdentity (CGI) of the candidate radio base station, or even the CellGlobal Identity (CGI) itself.

In a first example embodiment and mode, the method further comprises theserving radio base station issuing a transmission gap to the mobilestation (the transmission gap has a predetermined duration during whichthe mobile station is able to obtain the information from the candidateradio base station); and the mobile station obtaining the informationfrom the candidate radio base station during the transmission gap.

In a variation of the first example embodiment and mode, the mobilestation informs the serving radio base station that the mobile stationwill issue the at least one reading gap (with a predetermined durationduring which the mobile station is able to obtain the information fromthe candidate radio base station); and in response thereto, the servingradio base station issues the transmission gap to the mobile station.

In a second example embodiment and mode, the method further comprisesthe serving radio base station starting a transmission gap and allowingthe mobile station to obtain information broadcasted by the candidateradio base station; and, the serving radio base station terminating thetransmission gap upon receiving the information from the mobile station.

In a variation of the second example embodiment and mode, the mobilestation makes a request that the serving radio base station issue thetransmission gap; and upon making the request, the mobile station startsa reading gap for obtaining the information.

In a third example embodiment and mode, the method further comprises theserving radio base station issuing periodic transmission gaps of fixedlength to the mobile station (whereby, e.g., at least one of thetransmission gaps is aligned with a broadcast frame of the candidateradio base station in which the information is broadcast by thecandidate radio base station); and the mobile station obtaining theinformation during one of the period transmission gaps.

In a fourth example embodiment and mode, the method further comprisesthe mobile station issuing the at least one reading gap for obtainingthe information from the candidate radio base station and ignoringtransmissions from the serving radio base station during the readinggap. An augmentation of the fourth example embodiment and mode comprisesthe mobile station further recovering any frames lost during the atleast one reading gap by using a repeat request procedure.

Alternatively, non-receipt of predetermined reports from the mobilestation indicates that the mobile station has issued the at least onereading gap and accordingly modifying communications between the servingradio base station and the mobile station (e.g., by lowering priority oftransmissions to the mobile station or by ceasing allocation ofscheduling resources to the mobile station).

As a further aspect, the technology can further comprise the servingradio base station providing the information to a neighbor relation listhandler.

In an illustrated, example context or environment of use, the candidateradio base station belongs to a GERAN radio access network and theserving radio base station belongs to another radio access technology(e.g., UTRAN). Conversely, in another illustrated, example context orenvironment of use, the candidate radio base station belongs to a UTRANradio access network and the serving radio base station belongs toanother radio access technology

In another of its aspects the technology concerns a mobile stationconfigured for wireless operation in a telecommunications systemcomprising a serving radio base station and a candidate radio basestation. The mobile station (MS) comprises one or more transceivers anda mobile station measurement communication function. The one or moretransceivers are configured to implement wireless transmissions betweenthe mobile station and the serving radio base station and between themobile station and the candidate radio base station. The mobile stationmeasurement communication function is configured to obtain informationfrom the candidate radio base station during at least one reading gap,the information being either information for locating Cell GlobalIdentity (CGI) of the candidate radio base station or the Cell GlobalIdentity (CGI) itself of the radio base station. In an exampleimplementation, the mobile station measurement communication function isconfigured to obtain a first type of information from the candidateradio base station during at least one reading gap and to obtain secondtype of information from the candidate radio base station during atleast another reading gap, each reading gap being a time period in whichthe mobile station does not receive information from the serving radiobase station.

In another of its aspects the technology concerns a base stationconfigured for wireless operation in a telecommunications systemcomprising a serving radio base station and a candidate radio basestation, as well as a mobile station. The base station comprises atransceiver and a base station measurement communication function. Thetransceiver is configured to implement wireless transmissions betweenthe mobile station and the serving radio base station and between themobile station and the candidate radio base station. The base stationmeasurement communication function is configured to allow the mobilestation to obtain information from the candidate radio base stationduring at least one reading gap, the information being eitherinformation for locating Cell Global Identity (CGI) of the candidateradio base station or the Cell Global Identity (CGI) itself of the radiobase station. In an example implementation, the base station measurementcommunication function is configured to allow the mobile station toobtain a first type of information from the candidate radio base stationduring at least one reading gap and to allow the mobile station toobtain a second type of information from the candidate radio basestation during at least another reading gap, each reading gap being atime period in which the mobile station does not receive informationfrom the serving radio base station.

Some example embodiments can use a two-stage information acquisitionprocedure for acquiring the ultimate necessary information (e.g., CellGlobal Identity (CGI)) of the candidate base station. In the two stageinformation acquisition procedure, a first type of information is firstacquired from the candidate base station. The first type of informationis utilized to determine how to obtain a second type of information(e.g., the ultimately sought information, such as CGI) from thecandidate base station. Thus, in one example embodiment and mode, themethod comprises acts including the following: (a) the mobile stationobtaining a first type of information from the candidate radio basestation during at least one reading gap (the reading gap being a timeperiod in which the mobile station does not receive information from theserving radio base station); (b) using the first type of information todetermine how to obtain a second type of information broadcast by thecandidate radio base station; (c) the serving radio base stationallowing the mobile station to obtain the second type of informationbroadcasted by the candidate radio base station; and, (d) the mobilestation obtaining the second type of information from the candidateradio base station during at least another reading gap.

In the foregoing embodiment and method, wherein the first type ofinformation can be one or more of synchronization information of thecandidate radio base station; local identification information of thecandidate radio base station; information for locating Cell GlobalIdentity (CGI) of the candidate radio base station; and/or the CellGlobal Identity (CGI) itself.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments as illustrated in the accompanyingdrawings in which reference characters refer to the same partsthroughout the various views. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention.

FIG. 1 is a diagrammatic view of a telecommunications system operatingin conjunction with both a first radio access network having a firsttype radio access technology and a second radio access network having asecond type radio access technology.

FIG. 2 is a diagrammatic view of a telecommunications system operatingin conjunction with both a first radio access network having a firsttype radio access technology and a second radio access network having asecond type radio access technology.

FIG. 3 is a simplified function block diagram showing certain exampleaspects of a representative mobile terminal and radio access networknodes which are involved in an example inter-RAT/frequency handover.

FIG. 4 is a diagrammatic view showing communications between a servingradio base station, a mobile station (MS), and a candidate radio basestation pertaining to measurements performed for detection andidentification of inter-RAT/frequency neighbors, wherein the servingradio base station and the candidate radio base station belong todifferent RATs and/or frequencies.

FIG. 5 is a diagrammatic view illustrating that a mobile station (MS) isnot able to receive from a serving radio base station during a readinggap; that quality of service (QoS) [bandwidth and/or latency) maydegrade significantly for mobile stations with higher bandwidthrequirement or greater number of requested scheduling blocks (e.g.,mobile station B) compared to mobile stations with less bandwidthrequirements (e.g., mobile station A).

FIG. 6 is a graphical view showing that a inter-RAT/frequencymeasurement threshold may be set higher than the corresponding handoverthreshold.

FIG. 7 is a diagrammatic view showing illustrating of an exampleembodiment and mode wherein a transmission gap is set sufficiently long(e.g., worse case scenario) to find desired information.

FIG. 8 is a diagrammatic view showing illustrating of an exampleembodiment and mode wherein a transmission gap occurs until desiredinformation is obtained and reported (in FIG. 8, signaling delaysbetween the mobile station (MS) and the serving radio base station areomitted, but would result in the transmission gap to end being laterthan as indicated in FIG. 8).

FIG. 9 is a diagrammatic view showing illustrating of an exampleembodiment and mode which uses sliding transmission gaps.

FIG. 10 is a flowchart showing example, representative acts or stepsinvolved in an example two-stage information acquisition procedure.

FIG. 11 is a diagrammatic view showing communications between a servingradio base station, a mobile station (MS), and a candidate radio basestation pertaining to measurements performed for detection andidentification of inter-RAT/frequency neighbors, wherein the servingradio base station and the candidate radio base station belong todifferent RATs and/or frequencies; and particularly wherein the mobilestation (MS) measures frame number or scheduling information regardingthe information broadcasted by the candidate BS, computes a timeinterval when the CGI of the candidate radio base station will betransmitted, and notifies the serving RAT when the Cell Global Identity(CGI) will be measured.

FIG. 12 is a diagrammatic view showing communications between a servingradio base station, a mobile station (MS), and a candidate radio basestation pertaining to measurements performed for detection andidentification of inter-RAT/frequency neighbors, wherein the servingradio base station and the candidate radio base station belong todifferent RATs and/or frequencies; and particularly wherein the mobilestation (MS) measures the frame number of scheduling information, theserving radio base station computes a time interval when the Cell GlobalIdentity (CGI) of the candidate radio base station will be transmittedand notifies the mobile station (MS) when the Cell Global Identity (CGI)should be measured using a particular method.

FIG. 13 is a graph reflecting signal quality as a mobile station (MS)moves away from coverage of a serving radio base station into coverageof a candidate radio base station having a different radio accesstechnology (RAT) and/or different frequency.

FIG. 14 is a diagrammatic view showing how a mobile station (MS) mayalternate between a serving radio base station and a candidate radiobase station when carrying out inter-RAT/frequency measurements, andparticularly showing a case in which reading gaps occur with a certainperiod and the gap length is constant.

FIG. 15 is a diagrammatic view illustrating scheduling in E-UTRANwherein resources are allocated both in frequency and time to a mobilestation (MS).

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth such as particulararchitectures, interfaces, techniques, etc. in order to provide athorough understanding of the present invention. However, it will beapparent to those skilled in the art that the present invention may bepracticed in other embodiments that depart from these specific details.That is, those skilled in the art will be able to devise variousarrangements which, although not explicitly described or shown herein,embody the principles of the invention and are included within itsspirit and scope. In some instances, detailed descriptions of well-knowndevices, circuits, and methods are omitted so as not to obscure thedescription of the present invention with unnecessary detail. Allstatements herein reciting principles, aspects, and embodiments of theinvention, as well as specific examples thereof, are intended toencompass both structural and functional equivalents thereof.Additionally, it is intended that such equivalents include bothcurrently known equivalents as well as equivalents developed in thefuture, i.e., any elements developed that perform the same function,regardless of structure.

Thus, for example, it will be appreciated by those skilled in the artthat block diagrams herein can represent conceptual views ofillustrative circuitry embodying the principles of the technology.Similarly, it will be appreciated that any flow charts, state transitiondiagrams, pseudocode, and the like represent various processes which maybe substantially represented in computer readable medium and so executedby a computer or processor, whether or not such computer or processor isexplicitly shown.

The functions of the various elements including functional blockslabeled or described as “processors” or “controllers” may be providedthrough the use of dedicated hardware as well as hardware capable ofexecuting software in association with appropriate software. Whenprovided by a processor, the functions may be provided by a singlededicated processor, by a single shared processor, or by a plurality ofindividual processors, some of which may be shared or distributed.Moreover, explicit use of the term “processor” or “controller” shouldnot be construed to refer exclusively to hardware capable of executingsoftware, and may include, without limitation, digital signal processor(DSP) hardware, read only memory (ROM) for storing software, randomaccess memory (RAM), and non-volatile storage.

1.0 OVERVIEW

1.1 Architectural Overview Examples

FIG. 1 shows an example telecommunications system 10 operating inconjunction with both a first radio access network 12 and a second radioaccess network 14. In the example telecommunications system 10 of FIG.1, first radio access network 12 has a first type radio accesstechnology (RAT) and second radio access network 14 has a second typeradio access technology. In the non-limiting example shown in FIG. 1, itso happens that first radio access network 12 uses GERAN radio accesstechnology, while the second radio access network 14 uses UTRAN (orE-UTRAN) radio access technology. Both first radio access network 12 andsecond radio access network 14 are connected to an external core network16, such may be (for example) the Public Switched Telephone Network(PSTN) and/or the Integrated Services Digital Network (ISDN). The corenetwork 16 can comprise, or otherwise have access to, neighbor relationlist (NRL) handler 18.

Both first radio access network 12 and second radio access network 14comprise radio base stations, generically referred to as “basestations”, and optionally include a controlling node such as a basestation controller (BSC) or radio network controller (RNC) forsupervising one or more base stations. Whether one or both of firstradio access network 12 and second radio access network 14 include acontrolling node depends on specific architecture of the particularradio access network, since some radio access networks (such as E-UTRAN)have an essentially flat structure achieved by eliminating thecontrolling node(s) and consolidating various functions in the basestation, as previously explained. In the particular example shown inFIG. 1 in which first radio access network 12 is presumed for sake ofillustration to be a GERAN type radio access network and second radioaccess network 14 is presumed to be a UTRAN, supervising nodes areillustrated (albeit with broken lines to show their optional presence insome types of radio access networks).

The first radio access network 12 thus includes one or more base stationcontrollers (BSCs) 26.sub.G, with each base station controller (BSC)26.sub.G controlling one or more base stations (BTSs) 28.sub.G. In theexample shown in FIG. 1, base station controller (BSC) 26.sub.G isconnected to two base stations, particularly base station (BTS)28.sub.G-1 and base station (BTS) 28.sub.G-2. Each base station (BTS)28.sub.G is depicted in FIG. 1 as serving three cells C. Each cell C isrepresented by a circle proximate the respective base station. Thus, itwill be appreciated by those skilled in the art that a base station mayserve for communicating across the air interface for more than one cell,and that differing base stations may serve differing numbers of cells.The base station controllers (BSCs) 26.sub.G controls radio resourcesand radio connectivity within a set of cells, e.g., the cells C.sub.Gshown in FIG. 1. Each base station (BTS) 28.sub.G handles the radiotransmission and reception within one or more cells.

The second radio access network 14 includes one or more radio networkcontrollers (RNCs) 26.sub.U. For sake of simplicity, the UTRAN 14 ofFIG. 1 is shown with only one RNC node, although typically more than onesuch node is typically provided. The RNC node 26.sub.U is connected to aplurality of base stations (BS) 28.sub.U. For example, and again forsake of simplicity, two base station nodes—base station (BS) 28.sub.U-1and base station (BS) 28.sub.U-2—are shown connected to RNC 26.sub.U. Itwill again be appreciated that a different number of base stations canbe served by an RNC, and that RNCs need not serve the same number ofbase stations. As in GERAN network 12, in UTRAN network 14 for sake ofsimplicity each base station 28.sub.U is shown as serving three cells(each such cell being labeled at least partially as C.sub.U). In secondradio access network (UTRAN network) 14, the radio network controller(RNC) 26.sub.U controls radio resources and radio connectivity within aset of cells C.sub.U, while the base stations (BS) 28.sub.U handle theradio transmission and reception within one or more cells.

A wireless mobile station (MS) 30 is shown in FIG. 1. As used herein,the term “mobile station (MS)” generically encompasses both the notionof a mobile station and the notion of a user equipment unit (UE), aswell as other concepts as previously explained. As explained herein, oneof the base stations of one of the radio access networks (either firstradio access network 12 or second radio access network 14) serves as aserving base station for mobile station (MS) 30 and another of the basestations of the other of the radio access networks may be a candidatebase station for mobile station (MS) 30. Thus, for example, cellC.sub.G-2-3 of first radio access network 12 may be the serving basestation for mobile station (MS) 30, but in view of proximity and/orreception cell C.sub.U-1-1 may be a candidate base station. The conversecould also occur.

FIG. 2 shows another example telecommunications system 10′ operating inconjunction with both first radio access network 12′ and second radioaccess network 14′. In the example telecommunications system 10 of FIG.1, first radio access network 12′ operates at a first radio frequency(f1) while the second radio access network 14′ operates at a secondfrequency (f2). As in the FIG. 1 example, both first radio accessnetwork 12′ and second radio access network 14′ are connected to anexternal core network 16 which can comprise, or otherwise have accessto, neighbor relation list (NRL) handler 18.

The first radio access network 12′ optionally comprises one or more basestation controllers (BSCs) 26.sub.1 f, with each base station controller(BSC) 26.sub.1 f (when deployed) controlling one or more base stations(BTSs) 28.sub.1 f, the base stations (BTS) 28.sub.1 f serving cellsC.sub.1 f in much the same manner as in FIG. 1. Likewise, the secondradio access network 14′ optionally includes one or more radio networkcontrollers (RNCs) 26.sub.2 f, with each RNC node 26.sub.2 f (whendeployed) connected to one or more base stations (BS) 28.sub.2 f servingcells C.sub.2 f.

It should be appreciated that the technology described herein pertainsto one or both of the inter-RAT type of operation depicted in FIG. 1(comprising radio access networks of different radio technology accesstypes) and the inter-frequency type of operation depicted in FIG. 2(comprising radio access networks of different radio frequencies). Forthis reason the inclusive nomenclature inter-RAT/frequency is employed.The entire subsequent discussion including reference to ensuing figuresencompasses both types of operation, e.g., both inter-RAT andinter-frequency, unless specifically stated otherwise or clear from thecontext.

In view of the applicability of the technology both to inter-RAToperation and inter-frequency operation, FIG. 3 generically showsserving base station 28.sub.S and candidate base station 28.sub.C. Theserving base station 28.sub.S can belong to one type of radio accesstechnology, while candidate base station 28.sub.C can belong to anothertype of radio access technology. In such example, it does not make anydifference for the purpose of FIG. 3 as to what types of differing radioaccess technologies are employed in the radio access networks of servingbase station 28.sub.S and candidate base station 28.sub.C.Alternatively, serving base station 28.sub.S can belong to a radioaccess network (or base station) which operates at a first frequency,while candidate base station 28.sub.C can belong to a radio accessnetwork (or base station) which operates at a first frequency. Further,FIG. 3 shows serving base station 28.sub.S and candidate base station28.sub.C as (optionally) being connected to controlling nodes such as aBSC/RNC type node, and particularly to nodes 26.sub.S and 26.sub.C,respectively. FIG. 3 shows selected general aspects of mobile station(MS) 30 and selected functionalities of the serving base station28.sub.S and candidate base station 28.sub.C.

The mobile station (MS) 30 shown in FIG. 3 includes a data processingand control unit 31 for controlling various operations required bymobile station (MS) 30. The data processing and control unit 31 ofmobile station (MS) 30 includes mobile terminal inter-RAT/frequencyhandover function 40 and measurement communication function 42, thepurposes of which are described in more detail subsequently. Inaddition, the data processing and control unit 31 provides controlsignals as well as data to radio transceiver 33 connected to antenna 35.The measurement communication function 42 controls communications withserving base station 28.sub.S and candidate base station 28.sub.C whenrequesting or obtaining measurements or information (e.g., measurementsor information for potential handover purposes) are concerned. Theinter-RAT/frequency handover function 40 actually is invoked when it isdetermined that a handover is to occur.

By way of example and non-exhaustive description, both serving basestation 28.sub.S and candidate base station 28.sub.C as shown in FIG. 3comprise base station data processing and control unit 36, which isconnected to one or more base station transceivers (TX/RX) 38. Each basestation transceiver (TX/RX) 38 is connected to a corresponding antenna39, an appropriate one of which communicates over an air interface withmobile station (MS) 30.

The data processing and control unit 36 of each of serving base station28.sub.S and candidate base station 28.sub.C compriseinter-RAT/frequency handover function 50 and measurement communicationfunction 52. For example, serving base station 28.sub.S comprisesinter-RAT/frequency handover function 50.sub.S and measurementcommunication function 52.sub.S, while candidate base station 28.sub.Ccomprises inter-RAT/frequency handover function 50.sub.C and measurementcommunication function 52.sub.C, For each base station, the respectivemeasurement communication function 52 controls communications withmobile station (MS) 30 for requesting or obtaining measurements orinformation (e.g., measurements or information for potential handoverpurposes); the respective inter-RAT/frequency handover function 50 isinvoked when it is determined that a handover is to occur.

Any or all of mobile terminal inter-RAT handover function 40;measurement communication function 42; inter-RAT/frequency handoverfunction 50; and/or measurement communication function 52 can comprise acontroller or processor as those terms are expansively described herein.Although not specifically referenced at very juncture of discussion,these functions are involved in performing acts described herein and assummarized briefly above.

1.2 Example Operation Overview

FIG. 4 illustrates certain basic example, non-limiting acts or stepswhich comprise an inter-RAT/frequency measurement scenario.Inter-RAT/frequency measurements from certain mobile stations chosenusing the triggering condition(s) described in Section 2.0 are used todetect new inter-RAT/frequency neighbors, as illustrated in FIG. 4, act(1). The actual triggering condition(s) comprising, e.g., rules andthresholds, may be evaluated at the base station (BS) or the mobilestation (MS). In the former case, the base station (BS) receivesmeasurements from the mobile station (MS) and evaluates the triggeringconditions. In the latter case, the base station (BS) informs the mobilestation (MS) regarding the triggering conditions and the mobile station(MS) evaluates the conditions and starts inter-RAT/frequencymeasurements once they are triggered. In the measurement configurationsent from the base station (BS) to the mobile station (MS) (FIG. 4, act(1)), the base station (BS) may include information needed to performthe measurement [for example the Absolute Radio Frequency ChannelNumbers (ARFCNs) for GERAN BSs and ARFCNs and scrambling codes for UTRANBSs].

The mobile station (MS) measures the signal quality of surroundinginter-RAT/frequency base stations once the condition(s) in Section 2.0are triggered. As shown by act (2 a) of FIG. 4, the measurements areperformed during reading gaps (explained above) and (as shown by act (2b) of FIG. 4) each measurement result is reported to the serving basestation (BS) together with the local ID of the base station (BS). Thelocal ID can take the form, for example, of the Base Station IdentityCode (BSIC) for GERAN or the scrambling code for UTRAN.

If the serving base station (BS) has no prior knowledge of a neighborbase station (BS) with the reported local ID, the serving base station(BS) may send a CGI measurement request to the mobile station (MS), asillustrated by act (3) in FIG. 4. As illustrated by act (4 b) of FIG. 4,the mobile station (MS) measures the Cell Global Identity (CGI) of thecandidate base station (BS), using, e.g., one of the embodiments andmodes presented in Section 3.0, and (as illustrated by act (4 a))reports the Cell Global Identity (CGI) to the serving base station (BS).In an example embodiment, the mobile station measurement communicationfunction 42 can be configured to receive and send communications whichcomprise the acts of FIG. 4, including the acts of measuring the CellGlobal Identity (CGI) of the candidate base station (BS) as in act (4 b)of FIG. 4 and reporting the Cell Global Identity (CGI) to the servingbase station (BS) as in act (4 a) of FIG. 4. In an example embodiment,the base station measurement communication function 52 can be configuredto receive and send communications such as those shown in FIG. 4 andwhich enable or allow the mobile station to perform acts of FIG. 4.

Based on the inter-RAT/frequency measurement reports and the informationretrieved from the lookup, the candidate base station (BS) can be addedto the neighbor relation list (NRL) of the serving base station (BS). Asillustrated by optional act (5) of FIG. 4, the serving base station (BS)can inform an NRL handler, such as an Operation and Support System (OSS)or any other management node, about the newly detected candidate basestation (BS). As illustrated by optional act (6) of FIG. 4, the NRLhandler informs the candidate base station (BS) regarding the newneighbor relation. Upon being so informed, the candidate base station(BS) adds an entry corresponding to the serving base station (BS) in itsNRL.

2.0 INTER-RAT/FREQUENCY MEASUREMENT TRIGGERING

Different triggering criteria for inter-RAT/frequency measurements arepossible. Suggested criteria include but are not limited to thefollowing: a) Mobile stations with low data rates performinter-RAT/frequency measurements. Retransmissions due to poor channelquality may result in a greater actual transmitted data than required bythe services in the mobile station (MS). Therefore, the criterion forchoosing mobile stations for measurements must be based on the actualtransmitted UL and DL data rates to the mobile station (MS). b) Mobilestations with an estimated signal quality of the serving base station(BS) below a given threshold (see threshold C in FIG. 6) performinter-RAT/frequency measurements.

Considering criteria a) described above, recall from the discussionconcerning, e.g., FIG. 15, that a scheduling block (SB) is the smallestschedulable entity and that the base station (BS) may control the UL andDL transmissions including retransmissions for a particular mobilestation (MS). The impact on a service, e.g., video streaming, whenperforming inter-RAT/frequency measurements is smaller for mobilestations that require less number of scheduling blocks (SBs), as shownin FIG. 5. As such, mobile stations with a low average number ofscheduled scheduling blocks (SBs) should perform inter-RAT/frequencymeasurements.

The threshold used in criteria b) can either be the same threshold as isused for inter-RAT/frequency handover measurements (e.g., threshold A inFIG. 6), or it can be set higher than the handover threshold (e.g.,higher than threshold A of FIG. 6, such as threshold C in FIG. 6)) tomake sure that an inter-RAT/frequency neighbor is found before themobile station (MS) falls out of coverage.

The usage of the triggering criterion a) and b), and the setting of thethreshold used in criteria b) can vary with different situations. Forexample a newly deployed base station (BS) may have many unknownneighbors and in order to find them quickly both alternatives a) and b)could be used. In a newly deployed base station (BS) it may also besuitable to set the inter-RAT/frequency threshold (C in FIG. 6) higherthan the handover (HO) measurement threshold. For a base station (BS)that has been in the network for some time, most of the neighbors can beassumed to be found already and it may be enough to use only criteria b)with the same threshold as for handover measurements.

Furthermore, the threshold C can depend on the service, subscriptiontype, UE type etc. For example, Gold subscription users are assignedlower threshold C than ordinary subscription users to avoid bulkmeasurements to a larger extent.

3.0 CELL GLOBAL IDENTITY (CGI) MEASUREMENTS

Assume that the mobile station (MS) has reported a candidate basestation (BS) in another RAT/frequency and that the serving base station(BS) requests a CGI measurement (act 3 in FIG. 4). To measure the CellGlobal Identity (CGI) of a base station (BS) in another RAT/frequency,the mobile station (MS) has again to tune in to the frequency of thebase station (BS) and stop listening to the serving RAT/frequency forthe time needed to measure the desired information of the candidateRAT/frequency. To obtain the Cell Global Identity (CGI) of a candidatebase station (BS) it may be needed to first obtain synchronization, thenthe actual time when the CGI is transmitted needs to be obtained, andfinally the CGI can be measured. This technology suggests a number ofdifferent ways, e.g., different embodiments and modes, to handle themeasurements of information transmitted from a base station (BS) in adifferent RAT/frequency. As used herein, “measurements” can refer to anyand all entities or types of information, e.g., synchronization andlocal ID, that must be known in order to obtain the Cell Global Identity(CGI). Consequently, the embodiments and modes may be used to measureany information transmitted by a base station (BS) in a differentRAT/frequency, not only the Cell Global Identity (CGI).

3.1 First Embodiment/Mode (Method a)

In a first example embodiment and mode, also known as “method a” or“solution a” and illustrated in FIG. 7, the serving base station (BS)issues a transmission gap of length T, where T is the worst case time toobtain the desired information from the candidate base station (BS).During this gap the mobile station (MS) measures the desiredinformation. Note, this solution requires that the serving base station(BS) be aware of the worst case time T.

As a variation of the first example embodiment and mode, also known as“method d” or “solution d”, the mobile station (MS) informs the basestation (BS) that it will measure during a reading gap of length T. Theserving base station (BS) creates a transmission gap during this period.This method is a subset of method a), however, in this case the mobilestation (MS) initiates the transmission gap.

3.2 Second Embodiment/Mode (Method b)

In a second example embodiment and mode, also known as “method b” or“solution b” and illustrated in FIG. 8, the serving base station (BS)starts a transmission gap right after transmitting the measurementrequest to the mobile station (MS). During this gap, the mobile station(MS) measures the desired information. The transmission gap ends as soonas the serving base station (BS) receives the measurement result fromthe mobile station (MS). The gap will have the maximum length T, where Tis the worst case time to obtain the desired information. In contrast tosolution a), the length of T must not be known in advance.

As a variation of the second example embodiment and mode, also known as“method e” or “solution e”, the mobile station (MS) starts a reading gapright after sending a transmission gap message to the serving basestation (BS). The base station (BS) issues a transmission gap that endsas soon as the base station (BS) receives the measurement result fromthe mobile station (MS). This method is analogous to method b), however,in this case the mobile station (MS) initiates the transmission gap

3.3 Third Embodiment/Mode (Method c)

In a third example embodiment and mode, also known as “method c” or“solution c” and illustrated in FIG. 9, the serving base station (BS)issues periodic transmission gaps of fixed length where the mobilestation (MS) measures the desired information. Assume that the desiredinformation is transmitted periodically. Under certain conditions thetransmission gaps will slide relatively to the broadcast frames for thedesired information and eventually align with one of these broadcastframes.

3.4 Fourth Embodiment/Mode (Method f)

In a fourth example embodiment and mode, also known as “method f” or“solution f”, The mobile station (MS) issues a reading gap and ignorestransmissions from the serving RAT/frequency during this time in orderto perform inter-RAT/frequency measurements, without reporting this tothe serving base station (BS). During inter-RAT/frequency measurementsthe mobile station (MS) is not reachable. The network will experiencethe same behavior as if the mobile station (MS) was passing through ashadow region.

A serving base station (BS) can ensure that no SBs (DL and ULtransmissions) are allocated for a mobile station (MS) when it isperforming inter-RAT/frequency measurements. The methods a)-e) ensurethat no DL and UL transmissions occur during the time interval when themobile station (MS) is measuring another RAT/frequency and, therefore,is not able to communicate with the serving RAT/frequency. Methods a)-c)are initiated by the serving base station (BS), which is aware of thetime interval during which the mobile station (MS) is performinginter-RAT/frequency measurements. Methods d) and e) are initiated by themobile station (MS), which informs the serving base station (BS) that itwill carry out inter-RAT/frequency measurements.

Method f) may result in loss of radio frames, since the mobile station(MS) abruptly changes frequency in order to perform inter-RAT/frequencymeasurements. However, this is not expected to be significant problemsince any loss of frames is recovered using Hybrid Automatic RepeatRequest (HARQ). Further, a mobile station (MS) may be configured to sendCQI reports to the base station (BS). A mobile station (MS) that isperforming inter-RAT/frequency measurements may not be able to sendpre-determined reports (e.g., CQI reports and (N)ACKs) to the servingRAN. Further, the base station (BS) knows that the mobile station (MS)at some unknown time will stop listening to the serving base station(BS) in order to perform the inter-RAT/frequency measurements.Therefore, the lack of incoming pre-determined reports (e.g., CQIreports) form a certain mobile station (MS) and/or the knowledge that ameasurement request has been sent to the same mobile station (MS) (whichhas not yet reported the measurements results) can be used as anindication that the mobile station (MS) is currently performinginter-RAT/frequency measurements. As such, the scheduler may beconfigured such that it lowers the priority of transmissions to thatmobile station (MS) or does not allocate any scheduling blocks (SBs) tothat mobile station (MS). The consequence of this is that the dropprobability of radio frames to a mobile station (MS) performinginter-RAT/frequency measurements is lowered and that the scheduler canallocate SBs to other mobile station (MS).

4.0 MEASUREMENT ENHANCEMENTS/VARIATIONS

Some example embodiments can use a two-stage information acquisitionprocedure for acquiring the ultimate necessary information (e.g., CellGlobal Identity (CGI)) of the candidate base station. In the two stageinformation acquisition procedure, a first type of information is firstacquired from the candidate base station. The first type of informationis utilized to determine how to obtain a second type of information(e.g., the ultimately sought information, such as CGI) from thecandidate base station.

FIG. 10 shows example, representative acts or steps involved in anexample two-stage information acquisition procedure. Act 10-1 comprisesthe mobile station obtaining a first type of information from thecandidate radio base station during at least one reading gap. The firsttype of information can be any information which will facilitatedetermining how to obtain the second type of information. For example,the first type of information can be frame number or schedulinginformation broadcast from the candidate base station. The reading gapfor act 10-1 is a time period in which the mobile station does notreceive information from the serving radio base station. In an exampleimplementation of the FIG. 10 procedure, the serving radio base stationallows the mobile station to obtain the first type of informationbroadcasted by the candidate radio base station.

Act 10-2 of the example two-stage information acquisition procedure ofFIG. 10 comprises using the first type of information to determine howto obtain a second type of information broadcast by the candidate radiobase station. The determination can be made either by the mobile station(MS) (as in the example implementation described with respect to FIG. 11below) or by the serving base station (as in the example implementationdescribed with respect to FIG. 12 below).

Act 10-3 of the example two-stage information acquisition procedure ofFIG. 10 comprises the serving radio base station allowing the mobilestation to obtain the second type of information broadcasted by thecandidate radio base station. As used herein, the serving base station“allowing” the mobile station to obtain the second type of informationcan include the serving base station to permit or authorize the mobilestation to obtain the second type of information, but in at least oneembodiment the mobile station, although permitted or authorized, mayignore transmissions from the serving base station in order to obtaininformation from the candidate base station. Act 10-4 comprises themobile station obtaining the second type of information (e.g., the CellGlobal Identity (CGI)) from the candidate radio base station during atleast another reading gap.

One or a combination of the methods, presented in Section 3.0, can beused to measure desired information from base stations in otherRATs/frequencies. Moreover, the first type of information (acquired inact 10-1 of FIG. 10, for example) can be acquired using one of themethods of Section 3.0, and the second type of information (acquired inact 10-4 of FIG. 10, for example) can be acquired using another (e.g.,different) ones of the methods of Section 3.0. In other words, it is notnecessary that the same method be used to acquire the first type ofinformation (which is used to help locate the second type ofinformation) and the second type of information.

Inter-RAT/frequency measurements could give less disturbances of thecarried traffic to the serving base station (BS) if synchronizationinformation and possibly other measured information from the candidatebase station (BS) are used to find the time interval when the desiredinformation, e.g., Cell Global Identity (CGI), is transmitted. With thisinformation, for example method a) or b) as described in Section 3.1 andSection 3.2 can be utilized during this given time only, which leads toless or no disturbance of the ongoing traffic in the servingRAT/frequency. If the candidate base station (BS) synchronization is notalready known it can be found by using one of methods a)-f), asdescribed in Section 3.0.

Act 10-2 of FIG. 10 involves using the first type of information todetermine how to obtain the second type of information broadcast by thecandidate radio base station. Determining how to obtain the second typeof information can include calculating the transmission time intervalfor the desired information based on measurement results (the first typeof information), such as current frame number and possibly schedulinginformation, can be done either by the mobile station (MS) or by theserving base station (BS) provided that the needed information has beenreported by the mobile station (MS).

FIG. 11 illustrates an example scenario in which the mobile station (MS)informs its serving base station (BS) of the time interval when a methodfor inter-RAT/frequency measurements is used. For example, act 1 in FIG.11 shows the mobile station (MS) acquiring the frame number orscheduling information from the candidate base station. Act 2 of FIG. 11represents the mobile station (MS) advising the serving base stationthat the mobile station (MS) is using a particular method (representedgenerically as method “X” in FIG. 11) to measure the CGI during acertain time interval (represented by time interval “[a,b]” in FIG. 11).Act 3 of FIG. 11 shows the mobile station (MS) actually measuring oracquiring the CGI of the candidate base station during the time intervalthat was announced in act 2 of FIG. 11. Act 4 of FIG. 11 depicts themobile station (MS) informing the serving base station of the CGI whichwas acquired as a result of act 3 of FIG. 11.

FIG. 12 illustrates another example scenario, and particularly ascenario in which the serving base station (BS) instructs the mobilestation (MS) of the time interval when a method for inter-RAT/frequencymeasurements should be used. Act 1 of FIG. 12 shows the mobile station(MS) acquiring the frame number or scheduling information from thecandidate base station. Act 2 of FIG. 11 represents the mobile station(MS) advising the serving base station of information of the candidatebase station, such as the frame number, scheduling information, timealignment, etc. Act 3 of FIG. 12 depicts the serving base stationdirecting the mobile station (MS) to use a particular method(represented generically as method “X” in FIG. 12) to measure the CGIduring a certain specified time interval (represented by time interval“[a,b]” in FIG. 12). Act 4 of FIG. 12 shows the mobile station (MS)actually measuring or acquiring the CGI of the candidate base stationduring the time interval that was prescribed in act 3 of FIG. 12. Act 5of FIG. 12 shows the mobile station (MS) informing the serving basestation of the CGI which was acquired as a result of act 4 of FIG. 12.

As a further alternative, the mobile station (MS) may decide not toinform the base station (BS) regarding the time interval and simplystart measuring the desired information as proposed in method of Section3.4.

5.0 EXAMPLE IMPLEMENTATIONS 5.1 First Example

A first example implementation for measuring the Cell Global Identity(CGI) of a base station (BS) in another RAT/frequency is now described.Assume that the triggering condition(s) outlined in Section 2.0 has beensatisfied and the mobile station (MS) is to start inter-RAT/frequencymeasurements. Then the mobile station (MS) may need to synchronize andmeasure the signal quality of a candidate base station (BS). This isdone in the currently described example implementation using method c)in Section 3.3 with sliding transmission gaps. The serving base station(BS) may request the mobile station (MS) to measure the Cell GlobalIdentity (CGI) of the candidate base station (BS), i.e., act 3 in FIG.4. If the mobile station (MS) is at this state not aware of when theCell Global Identity (CGI) of the candidate base station (BS) will betransmitted, it attains the scheduling information using method f) inSection 3.4. The scheduling information may be based on the frame number(as in e.g., GERAN) or any other explicit scheduling informationbroadcasted by the candidate base station (BS) (e.g., UTRAN). The mobilestation (MS) then computes the time interval during which the CGI of thecandidate base station (BS) is transmitted and measures the CGI usingmethod f), meaning that the mobile station (MS) ignores transmissionsfrom the serving RAT/frequency during the measurement time.

5.2 Second Example

The second example pertains to retrieving CGI from a GERAN BS whileconnected to another RAT/frequency. In GERAN the CGI is transmitted onthe BCH. The TDMA frame number where the CGI will be transmitted isspecified in 3GPP TS 45.002, Multiplexing and multiple access on theradio path. By using for example method c) (in Section 3.0) with slidingtransmission gaps the FCCH for frequency fine-tuning and the SCH forsynchronization can be measured. When the SCH has been read, the mobilestation (MS) will know the current frame number. If the mobile has keptthe synchronization to the GERAN base station (BS) since the local IDwas measured, the current frame number is already known, and the mobilewill not need to perform additional measurements of FCCH and SCH.

Once the current frame number is known, the mobile station (MS) is ableto calculate the time interval to measure the CGI. This measurement isperformed using for example method f) (in Section 3.4), i.e. the mobilestation (MS) measures the CGI of the GERAN base station (BS) and ignorestransmissions from the serving RAT/frequency during the measurementtime. The mobile station (MS) then reports the measured CGI to the basestation (BS).

5.3 Third Example

The third example pertains to retrieving CGI from an UTRAN base station(BS) while connected to another RAT/frequency. In UTRA the CGI istransmitted on the Primary Common Control Physical Channel (P-CCPCH)3GPP TS 25.331, Radio Resource Control (RRC); Protocol specification.The radio frame in which the CGI is transmitted is given by the MasterInformation Block (MIB), which is also transmitted in the P-CCPCH. Themobile station (MS) must therefore first read the information containedin the MIB and then read the CGI.

The mobile station (MS) synchronizes and obtains the scrambling code ofthe candidate base station (BS) by using for example method c) (inSection 3.3) with sliding transmission gaps. When synchronized, themobile station (MS) starts reading the P-CCPCH and obtains the SystemFrame Number (SFN). The mobile station (MS) calculates the frame and thetime interval in which the MIB is transmitted using the SFN. The mobilestation (MS) reads the contents of the MIB, using for example method f)(in Section 3.4), and obtains the frame and the time interval in whichCGI is transmitted. The mobile station (MS) then reads the CGI using forexample method f) (in Section 3.4) and reports the CGI to the servingbase station (BS).

6.0 EXAMPLE ADVANTAGES

Automatic inter-RAT/frequency NRL management as described herein leadsto lower costs for the operators in planning and maintaining neighborrelation lists (NRLs), which are needed for seamless inter-RAT/frequencymobility. The advantages offered by this technology include (withoutlimitation): Very little or no human intervention is required whenestablishing neighbor relation lists (NRLs). The methods presented arebased on feedback information from the mobile stations and, as such, theautomatic NRL (ANRL) management is responsive to changes in radiopropagation conditions in the cell. Radio propagation models based on,e.g., topology, are not needed, since the invention relies on thefeedback information from mobile stations. Very small or negligibledisturbances are introduced in the carried traffic between the mobilestations and the base stations. A negligible traffic is introduced inthe transport network between the base stations compared to previousart, some of which rely on the base stations to continuously exchangeinformation regarding the mobile stations in their respective serviceareas. Inter-RAT/frequency NRL is supported in contrast to previousknown solutions that only address one particular RAT.

Although the description above contains many specificities, these shouldnot be construed as limiting the scope of the invention but as merelyproviding illustrations of some of the presently preferred embodiments.Therefore, it will be appreciated that the scope of the presentinvention fully encompasses other embodiments which may become obviousto those skilled in the art, and that the scope of the present inventionis accordingly not to be limited. Reference to an element in thesingular is not intended to mean “one and only one” unless explicitly sostated, but rather “one or more.” All structural and functionalequivalents to the elements of the above-described preferred embodimentthat are known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassedhereby. Moreover, it is not necessary for a device or method to addresseach and every problem sought to be solved by the present invention, forit to be encompassed hereby.

The invention claimed is:
 1. A method in a mobile station for cellglobal identity acquisition comprising the steps of: issuing a readinggap, the reading gap being a time period in which the mobile stationdoes not receive signals from a serving cell, the serving cell operatingon a first frequency; receiving, during the reading gap, data broadcaston a second frequency by a candidate cell; and acquiring from saidreceived broadcast data cell global identity (CGI) information for thecandidate cell, wherein said CGI information comprises one or more of: aCell Global Identity of the candidate cell, information for locatingsaid Cell Global Identity, and a local identity (ID) for the candidatecell.
 2. The method of claim 1, further comprising the steps ofreceiving from a radio base station serving the serving cell ameasurement gap and issuing the reading gap as at least part of thereceived measurement gap.
 3. The method of claim 1, further comprisingthe step of temporarily aborting a communication with a radio basestation serving the serving cell to set up the issued reading gap. 4.The method of claim 1, wherein the serving cell operates in a firstradio access technology and the candidate cell operates in a secondradio access technology.
 5. The method of claim 1, wherein the CGIinformation comprises said Cell Global Identity of the candidate cell.6. The method of claim 1, wherein the CGI information includes saidinformation for locating said Cell Global Identity.
 7. The method ofclaim 1, wherein the CGI information is local identification informationof a radio base station serving the candidate cell.
 8. The method ofclaim 1, further comprising the steps of: obtaining a first type ofinformation from the candidate cell during at least one reading gap;and, obtaining a second type of information from the candidate cellduring at least another reading gap, each reading gap being a timeperiod in which the mobile station does not receive information from theserving cell.
 9. The method of claim 8, wherein the first type ofinformation is information for locating Cell Global Identity of thecandidate cell.
 10. The method of claim 8, wherein the second type ofinformation is Cell Global Identity of the candidate cell.
 11. A mobilestation for global cell identity acquisition comprising: a memory; and aprocessor coupled to the memory, the processor being configured to:issue a reading gap, the reading gap being a time period in which themobile station does not receive signals from a serving cell, the servingcell operating on a first frequency; receive, during the reading gap,data broadcast on a second frequency by a candidate cell; and acquirefrom said received broadcast data cell global identity (CGI) informationfor the candidate cell, wherein said CGI information comprises one ormore of: a Cell Global Identity of the candidate cell, information forlocating said Cell Global Identity, and a local identity (ID) for thecandidate cell.